Calcium base grease containing a nickel



United States PatentO CALCIUM BASE GREASE CONTAINING A NICKEL,

LEAD OR LITHIUM SALT OF A DIALKYL DI- THIOPHOSPHORIC ACID DIESTER John Walter Nelson, Lansing, and Milton P. lileinholz,

Homewood, lll., assignors to Sinclair Refining Company, New York, N.Y., a corporation of Maine No Drawing. Application February 6, 1957 Serial No. 638,476

2 Claims. (Cl. 25232.7)

This invention relates to soap-thickened greases which are inhibited against oxidation. More particularly, this invention provides for the inhibition of anhydrous calcium l2-hydroxy stearate greases by the incorporation of certain oil-soluble metal salts of diester dithiophosphates.

It is generally known that certain of the metal salts of the diesters of dithiophosphoric acids impart desirable properties to mineral lubricating oils when added in minor amounts. Particularly, these salts afford increased resistance to oil oxidation and bearing corrosion as evidenced by Patent No. 2,364,283 to Freuler. However, the prior art has not generally made a distinction between the use of these additives in greases and fluid lubricating oils nor between the difierent types of grease-metal-salt combinations but apparently has acted upon the assumption that The problems concerned with the inhibition of oxidation in a fluid lubricating oil are normally diiferent from the inhibition of oxidation in a solid lubricating grease in that the grease is subjected to much higher stresses and localized temperatures next to bearing surfaces which in creases the tendency for oxidizing the base oil, such oxidation often being catalyzed by the thickening soap. Furthermore, among the various grease compositions there is found difierent so-called gel structures in each grease and subsequently unique problems existing in relation to each grease. Moreover, the soap used in thickening one type of grease composition may be more prone to deterioration than the soap used in thickening another type of grease composition and even if the two soaps are prone to deterioration in the same degree it has been found that the different metallic substituents used in the soaps can catalyze the oxidation of the oil component to varying extents. Thus, it has become highly important to learn as much as possible about the effect of each of the oxidation inhibiting agents in difierent soap thickened greases and to establish some definite correlation between the inhibiting agents and particular greases.

According to this invention, we have found that certain of the metal salts of the diesters of dithiophosphoric acids while known to act generally as oxidation inhibiting agents in fluid lubricating oils, do not give uniformly good results when added to dissimilar soap thickened greases.

2,899,388 Patented Aug. 11, 1959 ice Whether this can be attributed to the catalytic effect of the metals of the different metallic, soap thickening agents or to the inherently different gel structures of the greases or to other causes is unknown at the present time. More particularly, we have found that about 0.1 to 5.0% and preferably about 0.5 to 2.0% by weight of the oil-soluble nickel, lead and lithium salts of dialkyl dithiophosphoric acid diesters show excellent oxidationinhibiting charac teristics when added to anhydrous calcium l2-hydroxy stearate grease while little, if any, improvement of the oxidation inhibiting characteristics are realized if the same salts in the same proportions are used in a lithium 12- hydroxy stearate grease. Moreover, these nickel, lead and lithium salts in the above amounts are more effective in inhibiting the oxidative tendencies of anhydrous calcium 12-hydroxy stearate greases than many of the other phosphoric acid ester salts such as barium, zinc or vanadium dialkyl dithiophosphates or other commercially recognized oxidation inhibitors such as Ortholeum 300 (primarily a diphenylamine) The metal salts of the diester dithiophosphate can be prepared by any of the well-known processes, such as by reacting an alcohol with phosphorous pentasulfide to form a di-substituted sulfur containing phosphoric acid and subsequently neutralizing the acid with a metal oxide, hydroxide or carbonate. The organic substituents of the acid can be any alkyl of four to twelve carbon atoms, e.g. eight, providing the metal salts have sufiicient oil solubility to afford the desired oxidation inhibiting properties. Advantageously, the total number of carbon atoms in the two alkyl groups of the diesters will be about l2.to 18. Examples of useful alcohols are, Z-methylpentanol-l, decanol, hexanol, heptanol, Z-ethylhexanol, etc. In addition, mixtures of the alcohols can bevutilized if desired.

The effectiveness of various diester metal salts were evaluated in an anhydrous calcium 12-hydroxy stearate and a lithium l2-hydroxy stearate grease. These greases were comprised of a mineral base oil of lubricating viscosity, e.g. about 50 SUS at F. to 200 SUS at 210 F., thickened to grease consistency with calcium or lithium 12- hydroxy stearate. Usually the soap will be about 4 to 30% by weight of the total grease composition and can be made from any fatty source such as the corresponding acid ester or glyceride. The salts evaluated were the nickel, lithium, lead, barium, zinc and vanadium salts of di-(Z-ethylhexyl)-dithiophosphoric acid.

The anhydrous calcium 12-hydroxy stearate greases which are to be inhibited by our preferred salts can be prepared by any of the conventional methods, the following being but an illustrative example. The greases can contain various additive components other than the antioxidant, such as the corrosion inhibitors, etc. Usually, in commercial procedures, the additives are incorporated before milling.

Example I Twenty pounds of 12-hydroxy stearic acid, 10 pounds of water, and sixty pounds of mineral oil containing 2.9 pounds of hydrated lime previously slurried in part of this oil were mixed in a steam heated kettle at 100 F. The mineral oil used was an 82 SUS/ 100 F. blend of 3 80 volumepercent solvent treated Mid-Continent neutral and volume percent conventionally refinednaphthemc base Coastal stock. The temperature was raised gradually and at about 130 F. a pronounced thickening occurred indicating reaction. The initial formation of a smooth soap took place in the heterogeneous phase system at a temperature well below the melting point of the acrd, i.e., below about 160 F., as indicated by presence of a few solid acid flakes on the kettle walls where temperature was maximum. During formation of the smooth, homogeneously thickened mass in the temperature range 130 to 190 F. free water was rejected, appearing at the surface and edge of the reaction mass in the kettle. The separated free water changed from cloudy to clear, showing essentially complete reaction of the lime and acid. The temperature was raised from 190 F. to 225 F. to evaporate visible non-emulsified water in order topreclude later foaming. An additional five parts of the oil blend (based on weight of fatty acid employed) was incorporated while raising the temperaturefrom 225 to 240 F. Dehydration in the temperature range of 225 to 240 F. was accompanied by gradual, smooth gel formation. The temperature was then raised to about 250 to 255 F. and held one hour to insure complete dehydration after which the grease was cooled to 170 F. while incorporating the remainder of the oil (90 pounds). The grease was then milled at 170 F., 0.005 inch clearance and a flow rate of 1.5 pounds per minute in a conventional colloid mill.

In these evaluation tests, the anhydrous calcium 12- hydroxy stearate grease was prepared essentially as de scribed in Example I having 10.8% by weight calcium 12-hydroxy stearate incorporated therein. The lithium 12-hydroxy stearate greases used in these tests were prepared by charging the fatty component, the lithium base and a portion of the mineral lubricating oil base into a steam jacketed grease kettle and thoroughly mixing at 180 to 190 F. until saponification was substantially complete. The resulting soap concentrate was dehydrated at 300 to 320 F. After dehydration the heat was shut off and the remainder of the mineral lubricating oil base was blended with the soap concentrate. The constitutents were proportioned so as to give about 10.4% by weight of the lithium 12-hydroxy stearate in the final grease composition.

Both of the above greases were milled once on a Charlotte colloid mill, weighed into one-pound cans and heated overnight at 200 F. 1.0 percent by weight of each of the metal salts was weighed directly into the separate grease cans and the mixtures stirred with a motor driven stirrer until the salt was blended throughout the mixture. 1.0 percent by weight of Ortholeum 300, a well-known commercial oxidation inhibiting agent, containing a mixture of alkylphenylamines, principally diphenylamine was blended with each of the greases and used as a reference blend. The samples were tested by the Norman-Holfman oxidation test regular method (ASTM D-942-50) and the more severe bronze block method. These tests were terminated when the oxygen pressure dropped 55 pounds or after a run of 500 hours. The following table gives pertinent data relative to these grease compositions.

Lithium 12 Hydroxy Anhydrous Calcium 12 stearate Grease, Lbs. Hydroxy stearate PressureDrop/Hours Grease, Lbs. Pressure Metal of Salt Drop/Hours Regular Bronze Regular Bronze Block Block 35/500 /118 34/500 55/334 48/500 55/174 6/500 6/500 16/500 55/132 6/500 4/500 46/500 55/120 55/360 55/442 55/105 55/77 7/500 6/500 55/24 55/55 55/36 55/42 22/500 55/82 55/50 55/31 Ortholeum 300 16/500 86/500 10/500 11/500 From the above table, it will be noted that the nickel, lead and lithium salts of di-(Z-ethylhexyl)-dithiophosphate show a very pronounced improvement over the other metal-salts of the'same dithiophosphate in respect to the oxidationcharacteristics in both:the regular method and the bronze block method and a substantial improvement over the commercial inhibiting agent when incorporated in an anhydrous calcium 12-hydroxy stearate grease. Comparingthe results obtained in the anhydrous calcium 12-hydroxy stearate grease with those obtained in the lithium 12-hydroxy stearate grease, a substantially difierent effect is immediately noticed. Noneof the salts displayed any substantial oxidation inhibition in the bronze block method and thus were essentially useless in comparison with the commercial product while the lead salt was the only one which showed any oxidation inhibition in the regular method, this being no substantial improvement over the commercial product. All of the other saltswere inferior to the uninhibited sample or to the commercial product and in some instances apparently promoted oxidatron.

It is evident from an examination of this data that the selection of the proper metal dithiophosphate oxidation inhibiting agent depends both upon the type of grease utilized and the particular metal salt employed and that these may not be indiscriminately chosen it uniformly good results are to be obtained.

We claim:

1. A lubricating grease composition consisting essentially of a major portion of a base mineral lubricating oil thickened to grease consistency with anhydrous calcium 12-hydroxy stearate and about 0.1 to 5.0% by weight of an oil-soluble metal salt of a dialkyl dithiophosphoric acid diester, said alkyl groups containing about 4 to 12 carbon atoms, and the metal of said salt being selected from-the group consisting of nickel, lead and lithium.

References Cited in the file of this patent UNITED STATES PATENTS Freuler Dec. 5, 1944 Sproule etal. Aug. 19, 1952 

1. A LUBRICATING GREASE COMPOSITION CONSISTING ESSENTIALLY OF A MAJOR PORTION OF A BASE MINERAL LUBRICATING OIL THICKENED TO GREASE CONSISTENCY WITH ANHYDROUS CALCIUM 12-HYDROXY STEARATE AND ABOUT 0.1 TO 5.0% BY WEIGHT OF AN OIL-SOLUBLE METAL SALT OF A DIALKYL DITHIOPHOSPHORIC ACID DIESTER, SAID ALKYL GROUPS CONTAINING ABOUT 4 TO 12 CARBON ATOMS, AND THE METAL OF SAID SALT BEING SELECTED FROM THE GROUP CONSISTING OF NICKEL, LEAD AND LITHIUM. 